Would this be considered cheating in a relationship?

Alright. Sooo, I broke up with my boyfriend. Other than our own problems, he was kinda seeing my bestfriend. They lived on the SAME street (greaaaaat) so when I was/or wasnt around, she'd always be there or when im not around they'd be together. I've talked to him about it & he doesnt see the big deal & they are just ''friends''. Well I dont appreciate if I was your girlfriend any you're hugging my friend goodbye? Ummm, no. Its not like a polite little hug you do with people you see on Thanksgiving. Lmao. So yeah, I always felt like flirting would go on & they even lied about hanging out when I called & they OBVOUSLY were. They talked on the phone too. It was ''about me''? Mhm, you dont have hour conversations about me everyday. I can understand SOME talking, because she knows me im her bestfriend. I found it extremly un loyal, im a very loyal friend & hate being betrayed. So I had broken up with him, he moved to California. I stopped being my best friends friend, but we eventually made up. Then this summer while I was on vacation, I found out THEY had dated a little bit after me & him broke up. (not to mention I go to a diff school so I wouldn't of known) so I found out that news by accident. Some friend I got there. Horrible, its just absoloutley devistating. I didnt want to end it, I loved him, but ya know what? I cant stay with anyone who is unloyal. Thanks for your time reading !